JPH07157854A - Method for cleaning inside of snout of hot dip metal coating - Google Patents

Abstract

PURPOSE:To eliminate the trouble such as defective plating surface, especially a defective surface appearance due to an alloying reaction, by excluding the zinc fume produced on the surface of a plating bath when a steel sheet is dipped into a plating bath through a snout. CONSTITUTION:A circulating port and a section port 8 are confronted with the side face of a snout or vertically arranged to remove the zinc fume produced from the surface of a plating bath in the snout 2 where a steel sheet 1 is dipped into the bath 3 in the snout of hot-dip metal coating, and further a nozzle 13 is furnished to blow gaseous nitrogen downward against the steel sheet 1 passing above the bath surface in the snout 2. As a result, the flaws of a plated steel sheet due to zinc fume and scum are remarkably reduced, especially in the alloyed steel sheet, and a galvannealed steel sheet excellent in surface appearance is obtained.

Description

Detailed Description of the Invention

[0001]

The present invention relates to hot dip galvanizing, hot dip galvanizing, hot dip aluminum coating, hot dip galvanizing-
The present invention relates to a method and apparatus for cleaning an inside of a snout for hot metal plating such as aluminum alloy plating.

[0002]

2. Description of the Related Art Conventionally, as a hot dip metal plating method, a steel sheet to be plated is heated and annealed, an upper part thereof is connected to an annealing furnace, and a lower end thereof is passed through an inside of a snout immersed in the hot dip metal plating bath to form a hot dip metal bath. It is a method of obtaining a hot-dip metal-plated steel sheet by immersing it inside, changing the direction of travel by a pot roll in a bath and pulling it upward, and controlling the amount of hot-dip metal plating adhered by a gas drawing method. When the steel sheet is immersed in the plating bath through the snout portion, if foreign matter such as dust, scum, dross, fragments of annealing furnace refractory bricks, powder, etc. adheres to the steel plate surface or plating bath surface, plating surface defects and alloying Problems such as abnormal reaction occur.

In order to solve these problems, various methods have been conventionally proposed. For example, Japanese Patent Publication 2-25
As in Japanese Patent Publication No. 981 and Japanese Patent Publication No. 3-49981,
As described in JP-A-61-186463 and a method of preventing the generation of scum by setting an atmosphere of hydrogen and oxygen in the atmosphere to be introduced into the snout to an inert gas atmosphere having a specific concentration or less, dipping into the snout. Molten zinc is discharged toward the steel plate width direction from the discharge port arranged on one side in the width direction of the steel plate, and floating substances such as floating dross on the bath surface are stripped along the strip width direction in the other side of the snout width direction. To the side of
In addition, a method is known in which floating material is collected from the other end side to prevent steel plate plating defects due to floating dross in the snout.

Further, as in JP-A-4-276051 and JP-A-4-276052, an inert gas is applied on the plating bath surface from one end side to the other end side in the width direction of the steel plate immersed in the snout. By spraying the scum on the surface of the bath and discharging the scum on the other end to the outside of the snout, and the method of preventing the scum from adhering to the steel sheet and Japanese Patent Publication No. 60-2654. Thus, by providing a slit nozzle across the entire width of the steel plate below the surface of the molten metal plating bath and ejecting the molten plating solution toward the steel plate in the vicinity where the steel plate enters the plating bath, the surface of the plated steel plate is It is intended to prevent the adhesion of foreign matter.

However, each of the methods has its respective drawbacks, and cannot prevent foreign matter from adhering to the steel sheet.
That is, Japanese Patent Publication No. 2-25981 and Japanese Patent Publication No. 3-4
In the method according to the Japanese Patent Publication No. 9981, scum generation can be reduced but not completely eliminated by simply controlling the hydrogen and oxygen atmosphere gas composition in the snout, and if it is possible, it will adhere to the steel plate. However, there is a problem in that it is impossible to remove foreign matter that is brought in as a result and foreign matter that falls from the inner wall of the snout to the plating bath surface. In addition, JP-A-6
Although the effects of reducing the amount of foreign matter on the bath surface can be obtained by the methods of JP-A 1-186463, JP-A-4-276051 and JP-A-4-276052, the foreign matter is wiped from one end side to the other end side in the snout. There is a problem that foreign matter is not completely prevented from adhering to the steel sheet in part during the process.

Further, according to the method disclosed in Japanese Patent Publication No. 60-2654, it is necessary to eject the plating bath with a strong pressure in order to remove the foreign matter in the vicinity of the steel sheet. Since the plating droplets from the slit nozzles on both sides collide with each other, the effect of eliminating foreign matter is lost, and problems such as entrainment of foreign matter due to ripples in the plating bath surface occur.

[0007]

SUMMARY OF THE INVENTION The present invention solves the problems described above, and when a steel sheet is immersed in a plating bath through a snout portion, a reflux port and a suction port are provided on the side surface of the snout,
By removing zinc fume generated on the plating bath surface by suction, or in addition to this, by arranging a nozzle that blows nitrogen gas downward to the steel plate passing on the plating bath surface in the snout. The purpose of the present invention is to prevent plating surface defects from adhering to the steel sheet by foreign substances on the surface of the plating bath, and in particular to solve the problem of surface appearance associated with the alloying reaction.

[0008]

Means for Solving the Problems In order to achieve the above-mentioned objects, the gist of the invention is as follows: (1) A steel sheet is immersed in a plating bath at a snout portion of hot dip metal plating. A method for cleaning the inside of a snout of hot dip metal plating, characterized in that a reflux port and a suction port for removing zinc fume generated from the bath surface inside the snout are arranged facing each other on the side surface of the snout. (2) At the snout part of the molten metal plating, the steel plate is immersed in the plating bath. A reflux port and a suction port for removing zinc fume generated from the bath surface in the snout are provided above and below the side surface of the snout, and inside the snout. The method for cleaning the inside of a snout of hot dip metal plating, characterized in that a nitrogen gas spraying nozzle is arranged downward with respect to the steel sheet passing over the surface of the plating bath. (3) A steel sheet that passes over the surface of the plating bath with a reflux port and a suction port facing each other, or with a reflux port and a suction port provided in the snout where the steel plate is immersed in the plating bath at the snout portion of the molten metal plating. On the other hand, the apparatus for cleaning the inside of a snout for hot dip metal plating is characterized in that a nitrogen gas spray nozzle is arranged downward.

The present invention will be described in detail below with reference to the drawings. FIG. 1 is a vertical sectional view showing a plating process according to the present invention. In the continuous hot-dip galvanizing apparatus, as shown in FIG. 1, a steel sheet 1 discharged from a continuous annealing furnace passes through a snout 2 and is immersed in a plating bath 3 in a plating bath 5 and then passes through a pot roll 4 and a plating bath. 3. The gas wiping nozzle 6 outside the bath 3 wipes off the excessively deposited plating layer on the surface, so that the surface of the steel sheet 1 is plated with a predetermined thickness. When the alloying treatment is performed thereafter, an alloying heating device is provided.

[0010]

By the way, conventionally, in hot dip galvanizing, a small amount of Al is added to the plating bath in order to improve the adhesion of zinc to the steel sheet. This Al reacts with Fe precipitated from the steel sheet to form Fe ₂ Al ₅ and floats on the bath surface as so-called top dross. Further, on the bath surface in the snout, foreign substances carried from the furnace by the steel plate and floating foreign substances due to zinc vapor in the snout are present. All of these foreign substances are transported to the vicinity of the steel sheet by the surface flow from the snout wall surface toward the steel sheet caused by the penetration of the steel sheet into the bath, and adhere to the steel sheet. As a result, plating defects such as indentation defects due to non-plating and dross adhesion occur. Even if these are not the major causes, the following new problems arise.

That is, in particular, when the zinc-plated steel sheet adhered to the steel sheet due to the penetration of zinc vapor into the steel sheet bath by the zinc vapor in the snout is alloyed, the galvanized steel sheet directly adheres to the steel sheet and is alloyed. Of the steel sheet
When the foreign matter is diffused, the foreign matter is prevented from diffusing into the galvanized layer, resulting in a new problem of poor appearance. In order to solve these problems, zinc fume in the snout is removed to prevent the generation of floating foreign substances on the plating bath surface.

Although FIG. 1 shows the steps described above,
In such a process, in order to remove zinc fume in the snout 2, a reflux port and a suction port from the reflux pipe 7 and the suction pipe 8 are arranged so as to face the snout side surface, and a circulation flow is provided on the bath surface. Is formed, and the ascending flow from the bath surface is sealed, and zinc fume intrusion into the upstream furnace is prevented.
FIG. 2 is a detailed view of the lower part of the snout showing an embodiment according to the present invention. As shown in FIG. 2, by arranging the reflux pipe 7 and the reflux port 9 from the suction pipe 8 and the suction port 10 so as to face the snout side surface, the upward flow from the bath surface receives the lateral flow. The flow channel is twisted to form a circulating flow 11 on the bath surface, and this rising zinc fume flow is sucked through the suction port 10 to prevent zinc fume intrusion into the annealing furnace upstream. The suction speed in this case is 3 m / sec in linear flow velocity.
The above is preferable, and the diameters of the reflux port and the suction port are preferably close to the width of the snout, and the height from the bath surface is 500.
About mm is desirable.

FIG. 3 is a detailed view of the lower part of the snout showing another embodiment according to the present invention. As shown in FIG. 3, the reflux pipe 7
And the suction tube 8 are provided above and below the side surface of the snout. That is, the reflux position is provided above the suction position, is configured to form a flow that is against the upward flow of zinc fume, and is downward from the reflux port 9 with respect to the steel plate passing over the plating bath surface in the snout. The inflowing nitrogen gas is sprayed from a spray nozzle. The sprayed reflux is suction-filtered from the suction port 10 through the suction pipe 8 together with zinc fume generated from the bath surface inside the snout, and the filtered fume is discharged to the outside of the snout.

FIG. 4 is a sectional view showing the state where the recirculation gas of FIG. 3 is sprayed. That is, nitrogen gas is blown downward from the steel plate 1 onto the plating bath surface 3 in the snout from the nozzle 13 of the nitrogen gas blowing nozzle tube 12, and the scum floating on the bath surface in the snout is utilized by utilizing its reflection power. 14 is removed from the steel plate in the direction of the arrow to suppress the attachment of scum to the steel plate. Further, it is desirable that the suction amount (volume flow rate) be slightly larger (for example, 10% increase) than the blowing amount by the N ₂ scarf.

FIG. 5 is a plan view of the nitrogen gas blowing nozzle portion according to the present invention. FIG. 5 (A) shows a spray nozzle in which the spray nozzle faces the steel plate. Figure 5
(B) shows the spray nozzle in a state in which the spray nozzle angle is angled with respect to the width direction of the steel sheet. The spray nozzle angle is 30 to 60 ° downward with respect to the traveling direction of the steel plate.
Is desirable. Within this angle range, the snout bath surface has the least waviness and is the optimum angle. The distance from the tip of the nitrogen gas spray nozzle to the steel plate is preferably 50 to 300 mm. Further, it is desirable that the tip shape of the nitrogen gas blowing nozzle is slit-like and the blowing velocity is high.

FIG. 6 is a diagram showing the relationship between the linear flow velocity at the suction port and the defective product occurrence rate due to zinc fume according to the present invention. As shown in FIG. 6, the linear velocity at the suction port is 3 m / se.
It can be seen that in the case of c or more, the defective product occurrence rate due to zinc fume is extremely low. From this result, it is desirable that the linear flow velocity at the suction port is 3 m / sec or more.

[0017]

【Example】

Example 1 Using the device shown in FIG. 2, 0.8 mm (thickness) × 121
A 9 mm (width) steel plate is passed at a line speed of 80 mpm, and the rising flow from the bath surface receives the flow from the side and the flow path is twisted to form a circulating flow on the bath surface. The flow was sucked through the suction port to prevent zinc fume from entering upstream. The suction speed in this case is 5 in terms of linear flow velocity.
The height from the bath surface was 500 mm. The steel sheet is Zn-0.1-0.3% Al, the surface after being immersed in a hot dip galvanizing bath having a bath temperature of 460 ° C., plated, and wiped to a predetermined plating thickness, the hot dip galvanized steel sheet being alloyed. The appearance was observed. As a result, by applying the method of the present invention as compared with the conventional method having no suction port, the flaws of the plated steel sheet due to zinc fume and scum could be significantly reduced.

Example 2 Using the device shown in FIG. 3, 0.8 mm (thickness) × 121
A 9 mm (width) steel plate is passed at a line speed of 80 mpm, and the reflux position provided on the snout is provided above the suction position to form a flow that is counter to the upward flow of zinc fume, Nitrogen gas flowing from the reflux port is sprayed downward to the steel plate passing over the plating bath surface in the snout from the spray nozzle, and the generated zinc fume flow is sucked from the suction port, and zinc fume upstream Prevented intrusion. The suction speed in this case is 4m in linear velocity.
/ Sec, the height from the bath surface was 500 mm, the nitrogen blowing nozzle angle was 45 °, and the flow rate was 5 m / sec for N ₂ blowing nozzle per steel sheet direction nozzle of the snout. The steel sheet is Zn-0.1-0.3% Al, the surface after being immersed in a hot dip galvanizing bath having a bath temperature of 460 ° C., plated, and then wiped to a predetermined plating thickness, the hot dip galvanized steel sheet is alloyed. The appearance was observed. As a result, by applying the method of the present invention as compared with the conventional method without a suction port and a spray nozzle, it was possible to significantly reduce the flaws of the plated steel sheet due to zinc fume and scum.

[0019]

As described above, by sucking the zinc fume generated by the present invention, the defects of the plated steel sheet due to the zinc fume and scum are significantly reduced, and the hot dip galvanized steel sheet having an excellent surface appearance is obtained. It is possible to obtain the excellent effect.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a plating process according to the present invention,

FIG. 2 is a detailed view of the lower part of the snout according to the present invention,

FIG. 3 is a detailed view of a lower part of a snout showing another embodiment according to the present invention,

FIG. 4 is a cross-sectional view showing the state of spraying the reflux gas of FIG. 3;

FIG. 5 is a plan view of a nitrogen gas blowing nozzle portion according to the present invention,

FIG. 6 is a diagram showing the relationship between the linear flow velocity at the suction port and the defective product occurrence rate due to zinc fume according to the present invention.

[Explanation of symbols]

 1 Steel Plate 2 Snout 3 Plating Bath 4 Pot Roll 5 Plating Bath 6 Gas Wiping Nozzle 7 Reflux Pipe 8 Suction Pipe 9 Reflux Port 10 Suction Port 11 Circulation Flow 12 Nitrogen Gas Spray Pipe 13 Nitrogen Gas Spray Nozzle 14 Scum

Claims (3)

[Claims] 1. A reflux port and a suction port for removing zinc fume generated from the bath surface in the snout in which the steel plate is immersed in the plating bath at the snout portion of the hot dip metal plating are arranged facing each other on the side surface of the snout. A method for cleaning the inside of a snout of hot dip metal plating, which comprises: 2. A reflux port and a suction port for removing zinc fume generated from the bath surface in the snout in which the steel plate is immersed in the plating bath at the snout portion of the molten metal plating are provided above and below the snout side surface, A method for cleaning an inside of a snout for hot dip metal plating, characterized in that a nitrogen gas spray nozzle is arranged downward with respect to a steel sheet passing over a plating bath surface inside the snout. 3. A steel sheet is immersed in the plating bath at the snout portion of the hot dip metal plating, and a reflux port and a suction port are provided to face each other in the snout, or a reflux port and a suction port are provided and the steel plate passes over the plating bath surface. The apparatus for cleaning the inside of the snout of the molten metal plating is characterized in that the nozzle for blowing nitrogen gas is arranged downward with respect to the steel plate.